The present invention relates to glide height testing for detecting defects in a disc medium, and more particularly to a structure for electrically isolating the piezoelectric crystal on a glide height test slider to improve noise suppression.
In order to certify that a magnetic disc is adequately smooth for use in a disc drive system, glide height tests must be performed on the disc. Glide height testing is used to verify that a magnetic recording disc is able to accommodate a specified glide height. As the density of data recorded on magnetic discs continues to increase, the flying height of magnetic transducers with respect to the disc must be reduced. As a result, the magnetic recording discs must accommodate the lower glide height of the transducer and the slider supporting it. For example, in order to accommodate a glide height on the order of two millionths of an inch, a glide test must be able to detect defects in the magnetic recording disc which are on the order of one millionth of an inch.
In addition to the general requirement of reduced glide height, magnetoresistive (MR) heads, which utilize an active head element made of a thin layer of NiFe, are extremely sensitive to small physical defects in the surface of the disc, such as undulations of the disc surface and microscopic debris on the disc. When the MR head strikes a defect, there is a momentary frictional heating of the MR element, known as a thermal asperity. This heating effect increases the resistance of the MR head, which causes data errors and loss of information in reading the disc.
A common type of glide height testing is performed by utilizing a test slider having a piezoelectric element bonded thereon. When any part of the slider contacts a protrusion on the surface of the disc, the slider vibrates from the impact. The piezoelectric element bonded on the slider senses these vibration forces acting on the slider, and exhibits a voltage between its terminals representative of the forces experienced by the element. If the vibration force sensed by the piezoelectric element exceeds a predetermined design level, or if vibration occurrences exceed a predetermined design frequency, then the disc media under test is not adequately smooth to be used in applications at the glide height being tested. A critical shortcoming of previous piezoelectric glide height testers was the low resolution attainable due to the effects of electrical noise on the piezoelectric crystal. Noise may be picked up by the piezoelectric crystal from external sources in several ways, such as through the test arm and suspension, through the disc spindle and disc, and through the wires from the system electronics to the piezoelectric crystal. As a result, conventional piezoelectric sensors have been unable to detect defects in the disc medium with sufficient resolution to support the reduced flying height required for high data density applications.